Many computing devices today include a touch screen, which is a touch-sensing interface that can detect and process touch input on a display screen. A touch screen may facilitate user interaction with the computing device in a variety of ways. For example, a touch screen may enable a user to select content displayed on the computing device by simply touching that content with an object such as a body part (e.g., a finger) or an instrument (e.g., a stylus). As another example, a touch screen may enable a user to enter alphanumerical characters into the computing device via a virtual keyboard presented on the touch screen. Many other examples are possible as well. Touch screens may detect and process touch input using a variety of different technologies, including but not limited to resistive, capacitive, infrared, surface acoustic wave, frustrated total internal reflection, optical imaging, and acoustic pulse recognition.